This invention relates to a vapor absorption refrigerator and, more particularly, to a hermetically closed circulation type, vapor absorption refrigerator of outstanding corrosion resistance, where the essential constituent member of the refrigerator is highly protected from corrosion by forming an anti-corrosive film on the surface of the essential constituent member.
The hermetically closed circulation type, vapor absorption refrigerator is operationally kept at a pressure less than the atmospheric pressure and thus generally utilizes water as a cooling medium and an aqueous concentrated LiBr solution as an absorbing solution. Generally, with a higher concentration of the absorbing solution, a higher refrigeration efficiency of the vapor absorption refrigerator can be obtained. For example, at the component at the highest temperature in a double effect vapor absorption refrigerator, that is, at the regenerator, the absorbing solution has a temperature of about 160.degree. C. and an LiBr concentration of 62%. On the other hand, the corrosiveness of the aqueous LiBr solution upon metals increases with higher temperature and concentration. Thus, the essential constituent member of the refrigerator, particularly the regenerator, is vigorously corroded without adding an appropriate inhibitor to the absorbing solution.
The inhibitors so far often used are inorganic oxidizing agents, and chromates, nitrates, molybdates, tungstates, etc. are well known oxidizing agents. These oxidizing agents are used together with an alkali metal hydroxide as a pH-controlling agent and the corrosion of the essential constituent member is suppressed by formation of a film on the surface of the essential constituent member through their oxidizing action.
Thus, an oxidizing agent having a strong oxidizing action is desirable for effectively preventing the corrosion, and chromates and nitrates have been often used for this purpose. The molybdates have a weak oxidizing action and a very low solubility in the absorbing solution and thus it is difficult to obtain the necessary concentration for the film formation. Therefore, the molybdates are not satisfactory for forming a anti-corrosive film. Furthermore, the molybdates require much more time to form a stable anti-corrosive film, and the essential constituent member is exposed to corrosion long before the formation of the film, thereby generating a hydrogen gas and lowering the refrigeration efficiency. That is, it is difficult to obtain a satisfactory anti-corrosive effect.
It has been also proposed to use organic inhibitors, but it is difficult to form a rigid film on the surface of the essential constituent member. Furthermore, the organic inhibitors do not have a satisfactory heat stability and also are liable to undergo selective dissolution in a higher alcohol as added to improve the heat transfer effect, thereby lowering the anti-corrosive effect.
The vapor absorption refrigerators, absorbing solutions and protection of the vapor absorption refrigerators from corrosion are disclosed, for example, in Japanese Patent Publications Nos. 45-1711, 45-25954, 42-26917, 40-11550 and 60-29872. Particularly, anti-corrosive aqueous LiBr solutions are disclosed in Japanese Patent Applications Kokai (Laid-open) Nos. 53-25288, 58-224186 and 58-224187. This prior art is directed to oxidation of the surfaces of the constituent members of a vapor absorption refrigerator to form an anti-corrosive film and consequently control the corrosion of the constituent members. In other words, corrosion of iron-based materials for the constituent members under the most severe corrosion conditions and inhibitor effects have been thoroughly taken into account in the prior art and thus various inhibitors have been proposed. However, advance formation of an anti-corrosive film on the surface of the essential constituent member of a vapor absorption refrigerator, i.e. before the refrigerator is placed into the refrigerating cycle, or the structure of the film for effectively preventing corrosion of the essential constituent member has not been taken into account in the prior art. Thus, no satisfactory reliability has been obtained against the corrosion. Furthermore, single operation of a high temperature regenerator of the vapor absorption refrigerator with a specific film-forming solution to form an anti-corrosive film on the inside wall of the high temperature regenerator exposed to a vigorous corrosion has not been taken into account in the prior art.